1. Field of Invention
The present invention relates to a flat display panel having such a structure that a front protective plate is unitedly bonded to the viewer""s side surface of a flat display panel main body so as to improve mechanical strength of the flat display panel particularly plasma display panel (hereinafter referred to simply as PDP) main body to prevent breakage, and to decrease electromagnetic noises and near infrared rays generated from the flat display panel main body.
2. Discussion of the Background Art
In recent years, PDP having such advantages that a large screen panel can be prepared and clear full color display can be given, has attracted attention. PDP is to provide a full color display in such a manner that a phosphor is selectively discharged to emit light in a large number of discharge cells isolatedly formed between two glass plates. From this principle of emission, electromagnetic waves and heat radiation (near infrared rays) to be a factor in malfunction of other devices or generation of noises are discharged from the front of PDP, and accordingly it is required to shield such electromagnetic waves and heat radiation.
Heretofore, the following has been known to impart a function to cut electromagnetic waves and heat radiation (near infrared rays) to the flat display panel main body.
(A) JP-A-11-119666 discloses a display panel comprising a PDP main body, an electromagnetic wave shielding material bonded to the front of the PDP main body by means of a transparent adhesive, a transparent substrate bonded to the front of the electromagnetic wave shielding material by means of a transparent adhesive, and a heat radiation cutting layer provided between the transparent substrate and the PDP main body. As the electromagnetic wave shielding material, an electrically conductive mesh made of metal fibers or metal-coated organic fibers is used, and as the heat radiation cutting layer, a multilayer film comprising a base film and an oxide transparent electrode film and a metal thin film alternately laminated on the base film, is used.
(B) JP-A-57-21458, JP-A-57-198413, JP-A-60-43605, etc., disclose an optical filter provided with a near infrared ray shielding layer made of a resin composition obtained by dispersing an additive having a near infrared ray absorption property (near infrared ray absorbent) in a binder resin. A near infrared ray shielding layer having such a construction is easily formed, and its material is available at a relatively low cost.
(C) JP-A-2001-13877 discloses a flat display device comprising a PDP main body and an optical filter comprising a visible light reflectance adjusting layer, an impact-relieving component and a component which adjusts the color, shields radiation electromagnetic waves, and shields near infrared rays as well, disposed and bonded to the display side substrate of the PDP main body.
However, among the above-described prior arts, in (A), since an electrically conductive mesh is used as the electromagnetic wave shielding material, if the numerical aperture of the mesh is lowered to increase the electromagnetic wave shielding property, the mesh tends to shield light emitted from the PDP main body, whereby the light transmittance tends to decrease, and the clarity of the image may be impaired, and if the numerical aperture of the mesh is increased, although the light transmittance improves, the electromagnetic wave shielding property tends to deteriorate.
In the case where a near infrared ray shielding layer comprising a near infrared ray absorbent as in (B) is applied to the front protective plate to be unitedly bonded to the PDP main body, no near infrared ray shielding effect as designed may be obtained. For example, in the construction as disclosed in JP-A-11-119666, if a near infrared ray shielding layer employing a near infrared ray absorbent is provided instead of the heat radiation cutting film employing a metal material, the near infrared ray shielding property or the color tone of the transmitted light may change as before and after long-term lighting, such being disadvantageous.
In (C), the optical filter part to be bonded to the PDP main body is provided with the impact-relieving material made of e.g. a urethane resin type material which is transparent and has impact resistance, or an acrylic resin type material containing an acryl rubber type material, such being effective for prevention of scratches. However, the rigidity of the optical film itself can not be increased with such a resin layer, and if an external force is applied from the viewer""s side, the external force is applied to a front glass of the PDP main body, and the PDP main body may not sufficiently be protected.
Further, in a flat display panel such as PDP, if the front protective plate itself bonded to the front of the flat display panel main body is deformed when subjected to an external force from the viewer""s side, the external force may act on the front glass of the flat display panel main body, and the flat display panel main body may be broken, and its prevention is also important.
Accordingly, it is an object of the present invention is to provide a flat display panel comprising a flat display panel main body and a front protective plate having an electromagnetic wave shielding function and a near infrared ray shielding function unitedly bonded to the main body, which has a favorable and stable near infrared ray shielding effect and which can more securely prevent breakage of the flat display panel main body.
According to one aspect of the present invention, there is provided a flat display panel comprising a flat display panel main body, and a front protective plate which comprises an antireflection layer, a translucent electrically conductive layer containing a metal having an electromagnetic wave shielding property and a near infrared ray shielding property, a highly rigid transparent substrate made of a tempered glass or a semi-tempered glass and an adhesive layer laminated in this order, bonded to the viewer""s side surface of the flat display panel main body by means of the adhesive layer.
In the flat display panel, the flat display panel main body may be PDP.
The electrically conductive layer in the present invention may have such a construction comprising an electrically conductive multilayer film comprising an oxide layer and a metal layer alternately laminated, and an earth electrode connected to the electrically conductive multilayer film.
The metal layer is preferably one composed of Ag or one containing Ag as the main component and containing at least one of Pd, Au and Cu, and the oxide layer in the electrically conductive multilayer film is preferably one containing ZnO as the main component and containing at least one oxide of a metal selected from the group consisting of Sn, Al, Cr, Ti, Si, B, Mg and Ga.
The present inventors have further conducted extensive studies on a change in the near infrared ray shielding effect when the near infrared ray shielding layer containing a near infrared ray absorbent is applied to a front protective plate of a type to be bonded and united with a PDP main body, and as a result, have found that the surface temperature of the PDP main body at the time of lighting increases to a level of 60xc2x0 C. by the average temperature on the entire screen, and partially increases to so high as about 80xc2x0 C. at a point of continuous lighting, and that as shown by a heat deterioration resistance test of Reference Example 1 as described hereinafter, when a near infrared ray shielding film containing a near infrared ray absorbent is exposed to a high temperature of 80xc2x0 C., the optical properties significantly deteriorate.
The present inventors have further conducted extensive studies and as a result, have found that when a glass substrate is laminated on the surface of a PDP main body, the surface temperature decreases to a level of 40xc2x0 C. on the surface of the glass substrate, even at a portion where the temperature reaches 80xc2x0 C. on the surface of the PDP main body. They have further found that with respect to a near infrared ray shielding film containing a near infrared ray absorbent, no significant deterioration of the optical properties takes place when the heating temperature is so low as about 40xc2x0 C., as shown by a heat deterioration resistance test of Reference Example 2 as described hereinafter. The present invention has been accomplished on the basis of these discoveries.
Namely, according to another aspect of the present invention, there is provided a flat display panel comprising a flat display panel main body and a front protective plate which comprises a transparent substrate, an electromagnetic wave shielding layer, a near infrared ray shielding layer containing a near infrared ray absorbent, provided on one side of the transparent substrate, and an adhesive layer provided as the outermost layer on the other side of the transparent substrate, bonded to the viewer""s side surface of the flat display panel main body by means of the adhesive layer.
The flat display panel having such a construction is provided with a near infrared ray shielding layer and an electromagnetic wave shielding layer, whereby a near infrared ray shielding effect and an electromagnetic wave shielding effect can be obtained.
Particularly, a transparent substrate is interposed between a flat display panel main body and a near infrared ray shielding layer containing a near infrared ray absorbent, and this transparent substrate has a role as a heat buffering layer which reduces heat transmitted from the surface of the flat display panel main body to the near infrared ray shielding layer. Accordingly, even when the surface temperature of the flat display panel main body becomes high at the time of lighting, heat deterioration of the near infrared ray absorbent contained in the near infrared ray shielding layer can be prevented, whereby a favorable and stable near infrared ray shielding effect can be obtained.
Further, the near infrared ray shielding layer employing a near infrared ray absorbent is easily formed and its material is available at a low cost, whereby cost cutting can be attempted.
It is preferred to provide an antireflection layer as the outermost layer on one side of the transparent substrate of the front protective plate.
The flat display panel having such a construction is provided with an antireflection layer, whereby an antireflection effect can be obtained. Here, the antireflection layer may be provided so as to be the outermost layer of the front protective plate.
A layer other than the transparent substrate, highly rigid transparent substrate, electrically conductive layer, electromagnetic wave shielding layer, near infrared ray shielding layer, antireflection layer and adhesive layer of the present invention, such as a pollution preventing layer, may be provided on the outside of the front protective plate of the present invention, as the case requires.